Uranium and Fluoride Geochemical Pathways in Ulaanbaatar and Rural Mongolia

Uranium (Nuclear Minerals) / Related Environmental Issues

Date posted: 11/12/16

Grayson, et al., report that high uranium levels are known in Ulaanbaatar ash dumps, groundwater, construction materials and vegetation, and the high radon level in the city drinking water. Combustion of uranium-bearing coals is a cause, but natural sources of uranium may also be factors. Mongolian coals are important sinks for elemental enrichment by uranium and other heavy metals, and 24 Mesozoic, Permian and Carboniferous coals have U-content above 1 g per tonne. Coal ash wastes are U-enriched due to depletion of volatiles and are candidates for economic extraction of uranium and other valuable metals. Uranium in water often exceeds WHO drinking water guidelines and chronic poisoning or fatality of aquatic crustaceans is probable. The uranium concentration in some ash dumps is sufficient to envisage economic recovery through in-situ leaching. While coals and ash are U-sinks, over 2,000 soda lakes and sodic soils are U-drivers causing thousands of square kilometers of Mongolia to have elevated uranium levels, and the cause of elevated levels of fluoride, arsenic, selenium and other elements. Soda lakes and their remarkable ecosystems merit scientific study. The uranium concentration in some soda lakes is sufficient to envisage economic recovery by mining. Sulphate-reducing alkali extremophile bacteria are capable of reducing uranium (VI) to precipitate uranium (IV) oxide (UO2) as uraninite, while nitrate-reducing alkali extremophile bacteria can dissolve the uraninite into U (VI) solution. The soda lakes integrity depends on large-scale removal of calcium ions, sequestrated as hundreds of millions of tonnes of Ca-carbonates locked on the undersides of gravel clasts. Calcium depletion permits leaching of fluorspar veins across vast regions, and the elevated fluoride levels of well waters causes thousands of rural children to suffer from endemic dental fluorosis. Blanket surveys for dental fluorosis are warranted in all fluorspar districts.